The renal preglomerular microvasculature is critically involved in achieving the homeostatic functions of the kidneys, including the regulation of Na+ and H2O excretion. The primary Na+ retaining hormone, angiotensin II (AngII), acts via AT1 receptors (AT1R) to elicit preglomerular (and postglomerular) vasoconstriction. Engagement of the AT1R provokes G protein-mediated phospholipase C activation, eventually leading to the rise in intracellular Ca2+ concentration ([Ca2+]i) that fuels Ca2+/calmodulin-dependent activation of the contractile apparatus. AngII also exerts mitogenic effects on vascular smooth muscle through a phenomenon involving not only engagement of the AT1R but also consequent transactivation of the epidermal growth factor receptor (EGFR), leading to activation of a variety of protein kinases that ultimately result in altered expression of a variety of pro-mitogenic gene products. Signaling events downstream of the EGFR have been implicated recently in eliciting contraction of vascular smooth muscle from large arteries artery, and our preliminary data indicate that afferent arteriolar contractile responses to AngII involve tyrosine kinase(s), including the EGFR tyrosine kinase, and that this process contributes to the [Ca2+]i response. The proposed work will address the hypothesis that AngII-induced contraction of renal preglomerular microvascular smooth muscle involves AT1R-mediated initiation of a complex signaling network that includes c-Src-dependent EGFR transactivation, activation of Ca2+-sensitive tyrosine kinases, and phosphorylation of ion channels that contribute to the Ca2+ influx and the contractile response. We further postulate that up-regulation of EGFR-dependent pathways contribute to the exaggerated AngII-induced contractile responsiveness in hypertension. The validity of these postulates will be examined by addressing the following specific aims: 1) Determine the mechanism through which the AT1R transactivates the EGFR, 2) Determine the mechanism through which AngII-induced EGFR transactivation promotes Ca2+ influx, 3) Determine if EGFR transactivation-linked signaling events are prototypical for other preglomerular vasoconstrictors that act via G protein-coupled receptors (specifically, arginine vasopressin), and 4) Determine if the EGFR transactivation pathway contributes to exaggerated responsiveness to AngII in AngII-dependent hypertension. The experimental strategy will utilize molecular, pharmacological, biochemical and physiological approaches to clarify the role of tyrosine kinases in evoking agonist-induced constriction of the preglomerular microvasculature. This approach should expose the activity of specific tyrosine kinases in PVSMCs and their consequent influences on the regulation of arteriolar tone. Successful completion of this project should advance our understanding of the mechanisms through which AngII regulates renal microvascular tone, an important determinant of peripheral resistance, Na+ excretion and arterial pressure. Lay Summary: Angiotensin II is a potent regulator of blood pressure, acting in part through effects on microscopic blood vessels in the kidney organ. This work is exploring the mechanisms through which angiotensin II rapidly contracts muscle cells in kidney microvessels, focusing on processes previously thought to occur only in slower-developing growth responses. Completion of this project should advance our understanding of angiotensin II-dependent regulation of kidney function and blood pressure in health and disease. PHS 398 (Rev. 05/01) Page 2 Principal Investigator/Program Director (Last, first, middle): Carmines, Pamela, K